No, I think it is demonstrably toxic, even in deposits far underground laid down millions of years ago.
What we need is a large scale Coal Remediation project, something along the lines of the mobilization in this country during World War II.
Dig that stuff up, and BURN IT. The only way to be sure. Otherwise that stuff will be lingering around in places like Colstrip for centuries.
As a practical matter it could be used to power electrical generation power plants, that would be very reliable and very economical. Further, it would provide much needed revenue to local tax authorities, and excellent careers for thousand and thousands of rural Americans.
It could be mined for the Hg.
Then we could use the Hg to measure the Earth’s fever.
I’ve actually been to Colstrip. And Gilette and surrounding areas.
Best to get China to extinguish their vast coal seam wildfires.